Lately, an orthogonal frequency division multiplexing (OFDM) scheme becomes the major technology in a wireless communication system. The OFDM scheme is a digital modulation method for transmitting data at a high speed by dividing data and loading the divided data on a plurality of subcarriers having orthogonal relation with each others. Since the OFDM scheme allows multiplexing of further more subcarriers than a frequency division multiplexing (FDM) scheme, the OFDM scheme has high frequency efficiency and is durable for inter symbol interference (ISI) because of multipath. Therefore, the OFDM scheme is suitable for high speed data transmission. Particularly, the OFDM scheme has been selected for various wireless communication systems such as a wide range local area network (WLAN), a wireless metropolitan area network (WMAN), power line communication (PLC), digital audio broadcasting (DAB), and digital video broadcasting (DVB).
Since the OFDM scheme can obtain a high data transmission rate at a wireless communication system and has high durability even at a frequency selective fading channel, the OFDM scheme has been receiving attention for wireless communication system.
However, an OFDM signal has a significant large peak-to-average power ratio (PAPR) at a transmitter. It causes in-band distortion and out-band distortion at a high power amplifier (HPA) and deteriorates a bit error rate, finally. Therefore, it is major concern of related studies to reduce the signal distortion in the HPA by reducing the PARP of the OFDM signal.
There have been many studies made for reducing the PAPR of the OFDM signal, and various PAPR reduction methods have been introduced. Such PAPR reduction methods may be classified by two references.
At first, the PAPR reduction methods may be classified into an additive method and a multiplicative method by whether it is performed through addition or multiplication. For example, a selected mapping (SLM) method and a partial transmit sequence (PTS) method are the multiplicative method because an input symbol sequence is multiplied with a phase sequence in the SLM method and the PTS method. On the contrary, a tone reservation (TR) method or a clipping method is the additive method because a reference signal is added in the TR method and the clipping method.
Also, the PAPR reduction method may be divided into a decisive method and a probabilistic method. The decisive method is a method for limiting the PAPR of the OFDM signal below a predetermined threshold like the clipping scheme. However, the probabilistic method improves PAPR distribution characteristic of the OFDM signal, probabilistically. The probabilistic methods such as the SLM method and the PTS method generate a plurality of signals having the same information, select one having the smallest PAPR from the plurality of signals, and transmit the selected signal.
Although it is known that the SLM method has better performance than the PTS method when the same amount supplementary information is used, the SLM method requires a more computation amount than the PTS because it is required to increase the number of phase sequences to improve the PAPR reduction performance and the computation amount of the SLM method increase linearly as the number of phase sequences increases.